1. Field of the Invention
The present invention relates to a droplet ejecting apparatus configured such that a head unit which ejects droplets by driving of an actuator is mounted on a head holder via a reinforcing plate. Further, the present invention relates to a method for estimating a thickness of an adhesive layer which adheres the head unit and the reinforcing plate to each other.
2. Description of the Related Art
There is conventionally known an ink-jet recording apparatus, as a droplet ejecting apparatus of the above-described type, in which a recording operation is performed on a recording medium with ink droplets ejected by a head unit that is reciprocated while being opposed to the recording medium. The head unit is attached to a reinforcing plate as disclosed by Japanese Patent Application Publication No. 2005-161761, and is mounted as a unit with the reinforcing plate on a head holder. FIG. 10A is an explanatory view of the head unit and the reinforcing plate of the above-described conventional ink-jet recording apparatus. FIG. 10B is an explanatory view of the head unit to which the reinforcing plate is adhered, as seen from a lower side of the head unit. FIG. 11A is a cross-sectional view showing a cross section of FIG. 10B taken along a line A-A with a portion thereof omitted. FIG. 11B is an explanatory view of the reinforcing plate that is upwardly warped at its end portion.
As shown in FIG. 10A, the head unit 30 includes a cavity unit 50 in which a plurality of ink flow channels are formed and a piezoelectric actuator 40 bonded to an upper surface of the cavity unit 50. Ink supply holes 31a, 31b, 31c, 31d for supplying inks to the ink flow channels are formed in the head unit 30. As shown in FIG. 11A, the cavity unit 50 is constituted by eight plate members 31, 32, 33, 34, 35, 36, 37, 38 stacked on each other. The plate members are adhered to each other with adhesive sheets (not shown). The head unit 30 is fixed to a head holder (indicated at “9” in FIG. 3) via the reinforcing plate 60. The reinforcing plate 60 has effects of enhancing a rigidity of the head unit 30 and preventing a cross talk by suppressing vibrations of the cavity unit 50 which are generated upon driving of the piezoelectric actuator 40. The cross talk is a phenomenon that vibrations generated upon ejection propagate among rows of nozzles. The reinforcing plate 60 is wider than the head unit 30. The reinforcing plate 60 has an opening portion 60e for exposing the piezoelectric actuator 40 of the head unit 30 adhered to the reinforcing plate 60. Reference numerals 60a, 60b, 60c, 60d indicate ink supply holes for supplying the inks to the respective ink supply holes 31a-31d of the head unit 30.
The reinforcing plate 60 is adhered to the head unit 30 with an adhesive sheet 2. The adhesive sheet 2 has adhesive surfaces as upper and lower surfaces thereof and has a plan-view shape corresponding to a plan-view shape of the cavity unit 50. In a step in which the head unit 30 and the reinforcing plate 60 are adhered to each other, initially, the adhesive sheet 2 is pressed against a lower surface of the reinforcing plate 60. Then, an upper surface 31i of the head unit 30 is positioned to coincide with the lower surface of the adhesive sheet 2 and is pressed against the lower surface of the reinforcing plate 60.
Meanwhile, the present inventor has found that the adhesive sheet 2 has the effect of preventing the cross talk among the nozzles by absorbing, owing to a flexibility of a material of the adhesive sheet 2, the vibrations of the cavity unit 50 that is generated upon vibrations of the piezoelectric actuator 40. Further, the present inventor has found that a resonance phenomenon which adversely affects the suppression of the cross talk occurs if a thickness of the adhesive sheet 2 does not fall within a predetermined range.
Thus, the present inventor has had an idea that a control of the thickness of the adhesive sheet 2 is an important problem and decided to control the thickness in the following method. Initially, as shown in FIG. 11A, the cavity unit 50 to which the reinforcing plate 60 is bonded is placed on a stand for measurement, such that the reinforcing plate 60 is lower than the cavity unit 50. Then, a reference position H2 for measurement is set at a position higher than the cavity unit 50, and a distance D12 from the reference position H2 to a lower surface 60h of the reinforcing plate 60 is measured. Subsequently, a distance D11 from the reference position H2 to the cavity unit 50 (i.e., a nozzle surface 38p of a nozzle plate 38) is measured. Then, a thickness D13 of the cavity unit 50 including the adhesive sheet 2 is determined by subtracting the distance D11 from the distance D12 (D13=D12−D11). Next, a thickness D4 of the adhesive sheet 2 is determined by subtracting a designed or nominal thickness D14 of the cavity unit 50 from the thickness D13 (D4=D13−D14). Then, whether the thickness D4 of the adhesive sheet 2 falls within the predetermined range is judged.